---
title: "Field-level validation"
section: "build-a-backend/data"
platforms: ["android", "angular", "flutter", "javascript", "nextjs", "react", "react-native", "swift", "vue"]
gen: 2
last-updated: "2025-03-17T16:14:03.000Z"
url: "https://docs.amplify.aws/react/build-a-backend/data/field-level-validation/"
---

You can enable field-level validation in your model schema by chaining a `validate` function to the field.

## Examples

```ts title="amplify/data/resource.ts"
const schema = a.schema({
  Todo: a.model({
    content: a.string().validate(v => 
      v
        .minLength(1, 'Content must be at least 1 character long')
        .maxLength(100, 'Content must be less than 100 characters')
        .matches('^[a-zA-Z0-9\\\\s]+$', 'Content must contain only letters, numbers, and spaces')
    )
  })
  .authorization(allow => [allow.publicApiKey()])
});
```

## Supported validators

### String Validators
For `string` fields:

| Validator | Description | Parameters | Example |
| --- | --- | --- | --- |
| `minLength` | Validates that a string field has at least the specified length | • `length`: The minimum length required<br/>• `errorMessage`: Optional custom error message | `a.string().validate(v => v.minLength(5, 'String must be at least 5 characters'))` |
| `maxLength` | Validates that a string field does not exceed the specified length | • `length`: The maximum length allowed<br/>• `errorMessage`: Optional custom error message | `a.string().validate(v => v.maxLength(100, 'String must be at most 100 characters'))` |
| `startsWith` | Validates that a string field starts with the specified prefix | • `prefix`: The prefix the string must start with<br/>• `errorMessage`: Optional custom error message | `a.string().validate(v => v.startsWith("prefix-", 'String must start with prefix-'))` |
| `endsWith` | Validates that a string field ends with the specified suffix | • `suffix`: The suffix the string must end with<br/>• `errorMessage`: Optional custom error message | `a.string().validate(v => v.endsWith("-suffix", 'String must end with -suffix'))` |
| `matches` | Validates that a string field matches the specified regex pattern using the **Java regex engine**. See notes below. | • `pattern`: The regex pattern the string must match<br/>• `errorMessage`: Optional custom error message | `a.string().validate(v => v.matches("^[a-zA-Z0-9]+$", 'String must match the pattern'))` |

<Callout>

**Note:** Our schema transformer uses the Java regex engine under the hood. Because of how TypeScript processes string literals, you must quadruple-escape special regex characters in your schema. In a TypeScript string literal, writing `\\\\s` produces the string `\\s`, which is the correct form for the Java regex engine. If you write `\\s`, it produces `\s`, which is invalid. Therefore, for the `matches` validator, ensure you use quadruple-escaping. For example:
`a.string().validate(v => v.matches("^[a-zA-Z0-9\\\\s]+$", 'Content must contain only letters, numbers, and spaces'))`

</Callout>

### Numeric Validators
For `integer` and `float` fields:

| Validator | Description | Parameters | Example |
| --- | --- | --- | --- |
| `gt` | Validates that a numeric field is greater than the specified value | • `value`: The value the field must be greater than<br/>• `errorMessage`: Optional custom error message | `a.integer().validate(v => v.gt(10, 'Must be greater than 10'))` |
| `gte` | Validates that a numeric field is greater than or equal to the specified value | • `value`: The value the field must be greater than or equal to<br/>• `errorMessage`: Optional custom error message | `a.integer().validate(v => v.gte(10, 'Must be at least 10'))` |
| `lt` | Validates that a numeric field is less than the specified value | • `value`: The value the field must be less than<br/>• `errorMessage`: Optional custom error message | `a.integer().validate(v => v.lt(10, 'Must be less than 10'))` |
| `lte` | Validates that a numeric field is less than or equal to the specified value | • `value`: The value the field must be less than or equal to<br/>• `errorMessage`: Optional custom error message | `a.integer().validate(v => v.lte(10, 'Must be at most 10'))` |
| `positive` | Validates that a numeric field is positive | • `errorMessage`: Optional custom error message | `a.integer().validate(v => v.positive('Must be positive'))` |
| `negative` | Validates that a numeric field is negative | • `errorMessage`: Optional custom error message | `a.integer().validate(v => v.negative('Must be negative'))` |

<Callout>

**Note:** Currently, we only support validation on **non-array** fields of type `string`, `integer`, and `float`.

</Callout>